Limit gclient sync to 2 jobs at once.
Limit gclient sync to 2 jobs at once.

Hopefully this will alleviate external network pressure, but should also lower
the fleet's overall susceptibility to it.

R=dba@chromium.org, vadimsh@chromium.org
BUG=561772

Review URL: https://codereview.chromium.org/1492863003

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@297805 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build